In recent years, following the rapid development of digital cameras, mobile phones with a camera, and so on, there have been demanded miniaturization and pixel densification of optical goods including image sensors. Since the miniaturization of an image sensor causes deterioration of sensitivity, various considerations have been made for increasing the efficiency of incident light incorporation. For example, by providing a condenser lens (henceforth, referred to as a microlens) at the outermost part of an image sensor, light is condensed efficiently and thereby the lowering of sensitivity is prevented. Moreover, there has been proposed to inhibit the reflection of light caused by the refractive index difference between an air medium and a microlens by using a curable composition for a microlens antireflection film containing a titanium oxide particle coated with a metal element oxide, a curable compound, and a curing catalyst (see, for example, patent document 1). Furthermore, for the purpose of inhibiting the reflection of light caused by the refractive index difference between a euphotic part and a color filter, between a color filter and a microlens, etc., and planarizing steps of a base, various planarization films with controlled refractive indices have been used. As coating materials for such planarization films, there have been disclosed, for example, a siloxane-based resin composition obtained by hydrolyzing and condensing an alkoxysilane compound in the presence of metal compound particles (see, for example, patent document 2) and a thermal curable resin composition containing a fluorine-containing siloxane polymer having a fluorine-containing silane compound and an epoxy group-containing silane compound as copolymerization components (see, for example, patent document 3).
Such coating materials to be used for planarization film applications are required to have not only a characteristic to completely cover and planarize steps of a base but also sufficient adhesion to the surface of a substrate composed of a base metal or an inorganic substance, the surface of resin, and the surface of a device. It is known that such a material generally contains a silane coupling agent for improving adhesion (see, for example, patent document 4-5). However, addition of the silane coupling agents disclosed in these documents to siloxane-based resin compositions has failed to offer sufficient adhesion.    Patent document 1: JP 2005-283786 A    Patent document 2: JP 2007-246877 A    Patent document 3: JP 2007-119744 A    Patent document 4: JP 2003-43688 A (paragraph 0032)    Patent document 5: JP 2005-49691 A (paragraph 0109)